There is a continuing need for archival storage of information in condensed form for economy pf storage. In the past this need has been satisfied by microfilm and microfiche techniques. Information, such as printed or graphic matter, is stored on photographic film as microimages. The film is then developed, fixing the stored information such that is cannot be subsequently altered. There has arisen a need for a capability in archival storage for subsequent updating of the stored information. Photographic film is not suitable for such applications since the capability for updating the stored information ends with development.
Ohta et al, U.S. Pat. No. 3,971,874 issued July 27, 1976, teach an optical information storage material having a transparent substrate, a TeO.sub.x layer or a mixture of tellurium and vanadium or lead oxides deposited on the substrate with a protective layer thereover. The TeO.sub.x layer alone, or with vanadium or lead added, is light sensitive, darkening on exposure to light or upon contact heating. With subsequent exposure to light or heat the layer can be darkened in areas not previously darkened. The addition of vanadium oxide to the TeO.sub.x layer improves the erasure properties of the layer. This storage medium has the disadvantages that a temperature of over 700.degree. C. is required for evaporation of the light sensitive layer and that tellurium is a highly toxic material.
Thus it would be desirable to have a light sensitive layer in which information can be recorded and in which additional information can be subsequently recorded, which is non-toxic, and which does not require high temperatures in the preparation of the layer.